Electric generator

ABSTRACT

The present invention discloses a generator ( 1 ) able to generate either unidirectional current or bi-directional current. A rotatable disc ( 7 ) has a conductive track ( 9 ) and a ferromagnetic bridge ( 8 ). Brushes ( 12, 13 ) switchingly open circuit a coil ( 16 ) or connect the coil ( 16 ) to a load resistor (R). Movement of the disc ( 7 ) results in bridge ( 8 ) shunting a core ( 15 ) of the coil ( 16 ). This generates an emf in the coil ( 16 ). If the circuit is closed, current flows in the resistor (R). If the circuit is open, no current flows. The arrangement is such that current only flows when the bridge ( 8 ) approaches the magnet ( 14 )—not when the bridge ( 8 ) recedes from the magnet ( 14 ). Thus, only the magnetic attraction for the bridge ( 8 ) by the magnet ( 14 ) impedes the movement of the disc ( 7 ) as the bridge ( 8 ) recedes from the magnet ( 14 ) without the disc&#39;s movement also being impeded by generation of electric current at that time.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Stage entry of International ApplicationNo. PCT/AU02/00081, filed Jan. 25, 2002, the entire specification claimsand drawings of which are incorporated herewith by reference.

FIELD OF THE INVENTION

The present invention relates to electric devices including generatorswhich generate an electric current and electric motors.

BACKGROUND ART

Most electrical devices include a magnetic field and a magneticallypermeable structure which are involved in relative movement. During thatmovement there is normally a symmetrical motion in which magneticrepulsion during one part of the motion is disadvantageous and magneticretardation during another part of the motion is also disadvantageous.

The object of the present invention is to provide both an electricaldevice and a method of generating an electric current in which thedisadvantageous magnetic retardation is reduced.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there isdisclosed a method of generating an electric current, said methodcomprising the steps of:

-   -   1. creating a magnetic field extending from a first magnetic        pole to a second magnetic pole,    -   2. creating a first magnetically permeable path extending from        adjacent said first magnetic pole to adjacent said second        magnetic pole,    -   3. winding a coils about said first magnetic path,    -   4. connecting an electrical load across said coil,    -   5. connecting a switch means in series with said coil,    -   6. enabling a second magnetically permeable path to move        relative to said poles into a position between said first and        second magnetic poles to shunt said first magnetic path,    -   7. moving said second magnetically permeable path relative to        said poles out of said position between said first and second        magnetic poles, and    -   8. opening and closing said switch means so that said switch        means is closed when said second magnetic path is moving into        said position and opened when said second magnetic path is        moving out of said position.

In accordance with a second aspect of the present invention here isdisclosed an electrical device comprising a magnetic field means havingfirst and second magnetic poles between which a magnetic field extends,a first magnetically permeable path carrying a coil and extending fromadjacent said first magnetic pole to adjacent said second magnetic pole,and switch means connected in series with said coil, a secondmagnetically permeable path mounted for movement relative to said polesinto and out of a position between said first and second magnetic polesin which said second path shunts said first path, and means to closesaid switch means as said second path moves towards said position andopen said switch means as said second path moves out of said position.

BRIEF DESCRIPTION OF THE DRAWING

Two embodiments of the present invention will now be described withreference to the drawings in which:

FIG. 1 is a perspective, view of a single coil generator in accordancewith a fist embodiment of the present invention,

FIG. 2 is a schematic magnetic circuit diagram and current waveformillustrating a first half cycle of operation of the apparatus of FIG. 1,

FIG. 3 is a diagram similar to FIG. 2 but illustrating the other halfcycle of operation, and

FIG. 4 is a plan view of the disc of a multi-coil machine,

DETAILED DESCRIPTION

As seen in FIG. 1, a first embodiment of a generator 1 has a base plate2 on which is mounted a prime mover in the form of an electric motor 3.Clearly any other form of prime mover such as an internal combustionengine, turbine, hydraulic motor, or the like will suffice. The motor 3has a shaft 4 which is supported by bearings 5, 6.

An insulative, non-permeable disc 7 is mounted on the shaft 4 forrotation therewith. Set into the disc 7 is a ferromagnetic bridge 8 anda curved conductive track 9. Mounted on an insulative support 11 are apair of carbon brushes 12, 13. Mounted to the rear side of the disc 7,and thus indicated by broken lines in FIG. 1, is a U-shaped permanentmagnet 14 having a north pole N and a south pole S (FIG. 2). Oppositethe magnet 14 is a U-shaped magnetically permeable core 15 formed fromsteel laminations or the like and upon which is wound a coil 16.

The coil 16, brushes 12, 13 and an electrical load in the form ofresistor R are connected in series. It will be apparent to those skilledin the art that the track 9 and brushes 12, 13 function as a rotaryswitch which open circuits the the coil 16 or connects the resistor Racross it in accordance with the position of the disc 7. The track 9 andbrushes 12, 13 are so arranged that the coil 16 is connected to theresistor R whilst the bridge 8 is approaching the core 15 and whilst thebridge 8 and core 15 are aligned. However, as the bridge 8 begins toleave the core 15 with continued rotation of the disc 7, the brushes 12,13 are open circuited by the departure of the track 9 from underneaththe brushes 12, 13.

Turning now to FIGS. 2 and 3, the magnetic circuit formed by the core15, magnet 14 and bridge 8 is schematically illustrated. Although thebridge 8 is very thin in the direction perpendicular to the plane of thedisc 7, it has an appreciable extent in the plane of the disc 7 and thusa low reluctance. This is indicated in FIG. 2 by the bridge 8 beingdrawn larger than it would appear in cross-section.

When the bridge 8 is absents as illustrated in FIG. 3, the magnetomotiveforce of the magnet 14 causes a certain level of flux Φ2 to be presentin the core 15. Because of the relatively large air gaps in the absenceof the bridge 8, the magnetic circuit as illustrated in FIG. 3 has arelatively him reluctance. However, as seen in FIG. 2, with the bridge 8shunting the core 15, a relatively low reluctance path is available fromthe north pole N to the south pole S of the magnet 14 via the bridge 8and two relatively small air gaps. Thus essentially most of the magneticflux firm the magnet 14 is present as flux Ø1 in the bridge 8. Almost noflux passes through the core 15.

Largely because of the change in air gap sizes, the reluctance of themagnetic circuit in the configuration illustration in FIG. 2 is lessthan the reluctance of the magnetic circuit in the configurationillustrated in FIG. 3. That is, Φ1 is larger than Φ2.

As a consequence, the magnetic potential energy of the circuit in theconfiguration of FIG. 2 is less than that of the circuit in theconfiguration illustrated in FIG. 3. This may be illustrated by gentlyspinning the disc 7 by hand. The disc 7 will come to rest (normallyafter a few oscillations as the disc 7 slows) with the bridge 8positioned in line with the magnet 14 and core 15. That is, in theconfiguration illustrated in FIG. 2.

Expressed another way, as the bridge 8 approaches the magnet 14, thelower magnetic energy state of FIG. 2 will cause the bridge 8 to bedrawn towards the magnet 14. Similarly, as the rotation continues andthe bridge 8 moves away from the magnet 14 an effort is required tomaintain the rotation as the higher magnetic potential energy state(s)are attained. For each revolution the effort of removing bridge 8 fromthe magnet 14 is substantially equal to the impetus gained by the disc 7as the bridge 8 approaches the magnet 14.

As the bridge 8 approaches the magnet 14, defining a first half cycle, asteady flux Ø2 is in the core 15 and links the coil 16. As the bridge 8progressively shunts the flux in the core 15, the magnetic field in thecoil 16 collapses. Thus an electromotive force is generated in the coil16. Since the coil 16 is connected to the load resistor R via thebrushes 12, 13 and the track 9, a current flows in the coil 16 asillustrated in FIG. 2.

Conversely, as the bridge 8 moves away from the magnet 14, defining asecond half cycle, at first there is a small amount of flux in the core15, and the flux progressively increases to Ø2. Thus an electromotiveforce is generated in the coil 16. If the coil 16 were not open circuit,a current indicated by broken lines in FIG. 3 would flow (with reversepolarity to the current in FIG. 2). However, the brushes 12, 13 andtrack 9 are open circuit, so no current flows.

Thus, at this time, the disc 7 is only impeded by the attraction of themagnet 14 for the bridge 8. As a result, the impediment to continuedrotation of the disc 7 is at a minimum and the efficiency of thegenerator 1 is increased.

The current flowing in the coil 16 generates an induced magnetic flux inthe core 15 which increases the magnetic flux in the core 15. Thisinduced magnetic flux increases with increasing speed of the disc 7. Thespeed of the disc 7 reaches a critical speed, at which the magnitude ofthe induced flux is equal to the magnitude of the flux supplied by themagnet 14. Thereafter, increasing speed causes increased induced flux inthe core 15 and the device runs as a motor.

It will be appreciated that the current generated by the arrangement inFIG. 1 is unidirectional in that current is generated onlyintermittently. However, with the duplicated arrangement, as illustratedin FIG. 4, two bridges 8, 108 are provided together with two tracks 9,109, two pairs of brushes 12, 13 and 112, 113 and two pairs of coils 16,116 each with its corresponding magnet (14, 114). Thus with thearrangement of the disc 107 of FIG. 4, two pulses are generated for eachrevolution of the disc 107. Depending upon the relative phasing of thecoils 16, 116, the current supplied to the resistor R can be either 2pulses of the same polarity (i.e. unidirectional current) or 2 pulses ofopposite polarity (i.e. bi-directional current or AC).

That is, either DC current or single phase alternating current can begenerated. By providing 3 discs 107 rotates by 120° to each other on thesame shaft 4, three phase alternating current can be generated with the3 resistors being connected in either Y or delta configuration as iswell known to those skilled in the electric generating arts.

The foregoing describes only some embodiments of the present inventionand modifications, obvious to those skilled in the art can be madethereto without departing from the present invention. For example, thepermanent magnet(s) 14, 114 can be replaced by an electromagnet having amagnetic field generating current. The magnitude of the currentgenerated or the speed of the motor, can be controlled by controllingthe magnetic field of the device. For example, the field current of anelectromagnet replacing magnet 14 can be controlled. Other ways ofcontrolling the magnetic field include adjusting the size of air gaps inthe magnetic circuit or other arrangements to adjust the reluctance ofthe magnetic path by, for example, changing the size of the core 15.Alternatively, a small winding can be wound about the magnet 14 toincrease or decrease its magnetic field.

Furthermore, control can also be effected by utilizing a controlresistor in series with the coil 16 instead of the open circuit asdescribed above. As the resistance of such a control resistor isprogressively decreased from an initial very high value, so the currentgenerated, or motor speed, is decreased. Other control methods includeelectronically clipping the voltage in coil 16 and/or electronicallycontrolling the current in coil 16.

Similarly, rather than use a mechanical switch in the form of tracks 9,109 and brushes 12, 13, 112, 113, a solid state switch utilizing SCRs,thyristors, transistors, or even diodes can be employed. Such SCRs andthyristors can be triggered by stationary sensing coils in which triggercurrents can be generated by small auxiliary magnets carried by thediscs 7, 107. Also rather than a closed circuit/open circuit being usedas the switch means, a low resistance/high resistance circuit can beused instead.

Finally, although the disc 7, 107 is preferably rote in one direction asdescribed above, it will be apparent to those skilled in the art thatthe disc 7, 107 can be oscillated (as indicated by the broken line arrowin FIG. 1) rather than rotated. In one such embodiment, the stationaryend point of the oscillation would see the bridge 8 fully insertedbetween the magnet 14 and core 15.

The tern “comprising” (and its grammatical variants thereof) is used inthe inclusive sense of “having” or “including” and not in the exclusivesense of “consisting only of”.

1. A method of generating an electric current, said method comprisingthe steps of: 1, creating a magnetic field extending from a firstmagnetic pole to a second magnetic pole, 2, creating a firstmagnetically permeable path extending from adjacent said first magneticpole to adjacent said second magnetic pole, 3, winding a coil about saidfirst magnetic path, 4, connecting an electrical load across said coil,5, connecting a switch means in series with said coil, 6, enabling asecond magnetically permeable path to move relative to said pole into aposition between said first and second magnetic poles to shunt saidfirst magnetic path, 7, moving said second magnetically permeable pathrelative to said poles out of said position between said first andsecond magnetic poles, and 8, opening and closing said switch means sothat said switch means is closed when said second magnetic path ismoving into said position and opened when said second magnetic path ismoving out of said position.
 2. The method as claimed in claim 1including the step of rotating said second magnetic path.
 3. The methodas claimed in claim 2 wherein the rotation of said second magnetic pathis arcuate.
 4. The method as claimed in claim 3 wherein the rotation ofsaid second magnetic path is circular.
 5. The method as claimed in claim2 wherein said switch means is mechanical and said method includes thestep of operating said switch means in synchronism with said rotation ofsaid second magnetic path.
 6. The method as claimed in claim 1 andincluding a plurality of coils.
 7. The method as claimed in claim 6wherein for each coil a corresponding magnetic field and correspondingsecond magnetically permeable path are provided.
 8. The method asclaimed in claim 7 wherein the electric current generated isbi-directional.
 9. The method as claimed in claim 1 wherein the electriccurrent generated is unidirectional.
 10. The method as claimed in claim1 wherein said relative movement of said second magnetic path isoscillatory.
 11. A method as claimed in claim 1 wherein said switchmeans is electronic.
 12. A method as claimed in claim 11 wherein saidelectronic switch means is selected from the group consisting of SCRs,thyristors, transistors and diodes.
 13. A method as claimed in any oneof claims 1-12 wherein opening said switch means creates a highresistance circuit and closing said switch means creates a lowresistance circuit.
 14. An electrical device comprising a magnetic fieldmeans having first and second magnetic poles between which a magneticfield extends, a first magnetically permeable path carrying a coil andextending from adjacent said first magnetic pole to adjacent said secondmagnetic pole, and switch means connected in series with said coil, asecond magnetically permeable path mounted for movement relative to saidpoles into and out of a position between said first and second magneticpoles in which said second path shunts said first path, and means toclose said switch means as said second path moves towards said positionand open said switch means as said second path moves out of saidposition.
 15. The device as claimed in claim 14 wherein said second pathis rotatably mounted.
 16. The device as claimed in claim 15 wherein saidrotation is arcuate.
 17. The device as claimed in claim 16 wherein saidrotation is circular.
 18. The device as claimed in any one of claims14-17 wherein said switch means is mechanical and operable insynchronism with said movement of said second magnetic path.
 19. Thedevice as claimed in any one of claims 14-17 wherein said switch meansis electronic.
 20. The device as claimed in claim 19 wherein said switchmeans is selected from the group consisting of SCRs, thyristors,transistors and diodes.
 21. The device as claimed in any one ofclaims-14-17 wherein said switch means is switched between highresistance and low resistance states.
 22. The device as claimed in claim14 and including a plurality of coils.
 23. The device as claimed inclaim 22 and having for each coil a corresponding magnetic field, meansand a corresponding second magnetically permeable path.
 24. The deviceas claimed in claim 23 wherein the electric current generated isbi-directional.
 25. The device as claimed in claim 14 wherein theelectric current generated is unidirectional.
 26. The device as claimedin claim 14 wherein the movement of said second magnetically permeablepath is oscillatory.
 27. The device as claimed in claim 14 andcomprising an electric generator and having an electrical load connectedin series with said coil.
 28. The device as claimed in claim 14 andcomprising an electric motor.